The present invention relates generally to an improved method and apparatus for the application of powdered resins to threaded fasteners. More particularly, the invention relates to improvements in the methods and apparatus used to apply, collect, recycle and make up the powdered resins used in various fastener coating technologies.
There are now known to the art a wide variety of methods and apparatus for the application of resin patches and coatings on threaded fasteners. These patches and coatings perform a variety of functions, including, for example, locking, sealing, masking, and corrosion protection Examples of typical state of the art methods and apparatus are disclosed in U.S. Pat. Nos. 4,775,555; 4,815,414; 4,842,890; 4,865,881; 5,090,355; and 5,571,323.
Powdered resin handling is an important aspect of this technology. For example, it is necessary to apply the resin uniformly to a large number of individual fasteners in a typical production run, and to maintain generally uniform powder specifications. It is also very desirable to collect and recycle the resin that does not adhere to the fasteners in the application processes. Various powdered resin handling systems are shown in U.S. Pat. Nos. 5,718,945; 5,908,155; and 6,209,758.
One drawback with existing technology, however, is that over time the powdered resin which has been continually recycled tends to degrade and the quality of the resulting patch or coating may be adversely effected.
Another problem associated with the existing technology is that some of the powdered resin may find its way into the immediate surroundings, requiring periodic equipment clean-up and even air cleaning equipment to reduce in-plant airborne resin.
There is also a need to introduce fresh or new powdered resin into the powder handling system, and the existing technology may suffer from the inability to intimately and uniformly mix the new powdered resin with that already circulating within the system or, alternatively, may achieve appropriate mixing but only through the use of costly mixing equipment
The present invention is directed to an improved method and apparatus for the application of powdered resins to threaded fasteners. In accordance with the present invention, the powdered resin handling system used to apply, collect, recycle and make-up the resin is generally enclosed; that is, with the exception of the application of the resin to the fasteners, the resin is generally maintained within conduit, housings or hoppers that are not open to the surroundings. This tends to minimize discharge of resin into the areas surrounding the fastener processing equipment and also isolates the resin from external environmental conditions that tend to degrade the resin over time. In addition, the present invention introduces fresh, new or make-up resin in a manner that assures intimate and thorough intermixing of the new and recycled resin while minimizing the cost and complexity of the equipment employed for that purpose.
In accordance with one embodiment of the invention, an apparatus is provided for the application of a powdered resin to fasteners comprising: a pressurized air-powered applicator having a pressurized air input and a powdered resin input, said applicator discharging an airborne powdered resin stream; a conveyor positioned to transport a plurality of fasteners through said resin stream; a vacuum nozzle positioned to collect overspray resin from said resin stream; a new resin supply container having a first conduit with a free end positioned to introduce new resin at or adjacent the vacuum nozzle thereby creating a new and recycled resin mixture; a bag collector in communication with said vacuum nozzle; a housing for enclosure of the bag collector, said housing having at least one discharge port for exhausting air passing through said bag collector; and a resin mixture supply container positioned to receive said resin mixture from said bag collector and having a second conduit that communicates with said powdered resin input to said resin applicator.
In accordance with another embodiment of the invention, a method is provided for applying a powdered resin coating onto fasteners comprising the steps of: generating an airborne powdered resin stream from a nozzle; passing a plurality of fasteners through said resin stream to apply said coating; collecting powdered resin overspray from said resin stream by means of a vacuum nozzle; introducing new powdered resin into said vacuum nozzle thereby forming a new and recycled resin mixture; collecting the resin mixture in a bag collector enclosed within a housing and filtering the air discharged from said housing; and transferring the resin mixture from the bag collector to an input to said nozzle.